The present invention relates generally to a slender carbon electrode and, more particularly, to a successively joinable carbon electrode utilizable for gouging or blasting metallic articles.
Various types of successively joinable carbon electrodes utilizable for gouging or blasting steel or other metallic articles are currently available in the commercial market. However, all of them still leave much room for improvement as will be discussed later. As is well understood by those skilled in the art, the essential requirement the joinable carbon electrode must satisfy is that, when one carbon electrode is coaxially connected with another, both the physical connection and the electrical connection must be firmly established simultaneously at the joint therebetween. If the electrical connection at the joint between one carbon electrode and another is unsatisfactory, the electrode assembly or torch composed of coaxially connected carbon electrodes would not withstand the applied electrical current of 500 to 1,500 amperes, resulting in heating of the joint until it becomes red hot. Once this happens, a portion of the connected carbon electrode at the joint become oxidized, resulting in consumption of that portion of the electrodes at the joint and then resulting in breakage of the carbon electrode torch. On the other hand, if the physical connection at the joint is unsatisfactory, there is a possibility of accidental separation of one carbon electrode from another, resulting not only in a potential hazard to one or more attendant workers, but also in an uneconomical way of use of the carbon electrodes.
So far as the carbon electrodes of the type now under discussion are currently manufactured on a mass-production basis, much difficulty has been found in satisfying both the firm physical connection and the firm electrical connection between one carbon electrode and another. In other words, because of the presence of deviations in dimensions among carbon electrodes having been ground during the manufacture thereof and because of the presence of deviations in film thickness of copper layers having been applied on the carbon electrodes, either the physical connection or the electrical connection between one carbon electrode and another tends to fail.
In order to ensure both firm physical and electrical connections at the junction between the carbon electrodes, various methods have heretofore been employed. One method is to employ a tubular copper coupling for each joint. Another method is to knurl a projection of the carbon electrode to be inserted into a socket in another carbon electrode so that a series of small ridges or protuberances on that projection of the carbon electrode can be crushed upon insertion into the socket in such another carbon electrode. A still another method is to form a split in the socket so that the latter can be spread during the insertion of the projection thereinto to absorb a difference in dimensions between the socket in one carbon electrode and the projection in another carbon electrode.
Since the present invention pertains to the carbon electrode of the type using the split described above, the prior art carbon electrode of the same type will be now described in detail with particular reference to FIGS. 1 to 4 of the accompanying drawings.
Referring first to FIG. 1, the prior art carbon electrode comprises an elongated body 1 of circular cross-section made of carbon and having a copper layer 2 coated on the outer peripheral surface thereof. The carbon body 1 has one end integrally formed coaxially with an outwardly tapered connecting projection 3, only a portion of the connecting projection 3 adjacent the carbon body 1 being exteriorly coated with a copper layer 4 which is continuous to the copper layer 2 on the carbon body 1. In practice, this connecting projection 3 is formed by grinding one end of the carbon body 1. The other end of the carbon body 1 is formed into a socket 5 adapted to receive the connecting projection of another carbon electrode of a construction identical with that shown, said socket 5 comprising an inwardly tapered bore portion 6 and a cylindrical opening portion 7 which is coated interiorly with a copper layer 8 continuous to the copper layer 2 on the body 1. The carbon body 1 has a slit 9 therein and extending axially inwardly from said other end of the carbon body, the length of which is larger than the depth of the socket 5, said slit 9 being partially cut throughout the wall of the carbon body 1 defining the socket 5.
When the carbon electrodes of identical construction as shown in FIG. 1 are connected together with the connecting projection 3 of one of them inserted into the socket 5 of the other of them in a manner shown in FIG. 2, both of the physical and electrical connections between these carbon electrodes can be established firmly and satisfactorily. In this condition shown in FIG. 2, not only is the connecting projection 3 depicted as firmly fitted into the socket 5, but the copper layer 4 on the connecting projection 3 is depicted as electrically connected to the copper layer 8 inside the cylindrical portion 7 of the socket 5, thereby satisfying the previously described requirement. Accordingly, only when the carbon electrodes are connected together in the fashion shown in FIG. 2, is there neither a possibility of occurrence of a red hot state at the joint during use nor a possible accidental separation of the carbon electrodes from each other and the resultant electrode torch can exhibit a satisfactory performance. This is primarily because of the function of the slit 9. The function of said slit 9 is, however, limited and it often happens that the carbon electrodes are connected together in a fashion shown in either FIG. 3 or FIG. 4.
The condition shown in FIG. 3 occurs either where the diameter of the connecting projection 3 of one carbon electrode is larger than that of the socket 5 of another carbon electrode, or where the copper layers 4 and 8 have an insufficient film thickness. In this case, when the projection 3 of such one carbon electrode is inserted into the socket 5 in such another carbon electrode, the split 9 is spread axially laterally of the carbon body 1, consequently expanding the copper layer 8 in the socket 5 radially outwardly to such an extent that the copper layer 4 on the connecting projection 3 being inserted into the socket 5 can no longer electrically connect to the copper layer 8 in the socket 5. This in turn results in the occurrence of the red hot state at the joint of the electrode torch.
On the other hand, the condition shown in FIG. 4 occurs either where the diameter of the connecting projection 3 of one carbon electrode is smaller than that of the socket 5 of another carbon electrode, or where the copper layers 4 and 8 have an excessive film thickness. In this case, insertion of the projection 3 into the socket 5 does not bring about a satisfactory carbon-to-carbon contact between the carbon electrodes so connected together and, accordingly, the carbon electrodes so connected tend to separate from each other during use.
The occurrence of both of the conditions shown in FIGS. 3 and 4 is attributable to the fact that the connecting projection 3 and the socket 5 are tapered in a complementary relationship to each other. More specifically, the reason for the occurrence of the condition of FIG. 3 is that, when the connecting projection 3 of one carbon electrode is inserted into the socket 5 of another carbon electrode, the socket 5 is generally radially outwardly enlarged with the consequent radially outward enlargement of the copper layer 8. On the other hand, the reason for the occurrence of the condition of FIG. 4 is that, since both the connecting projection 3 and the socket 5 are tapered, and since the stroke over which the projection 3 is moved during insertion thereof into the socket 5 is limited, no carbon-to-carbon contact is attained between the carbon electrodes.
The above description concerning the prior art carbon electrode shown in FIGS. 1 to 4 applies to what is disclosed in, for example, the Japanese Utility Model Publication published on Mar. 24, 1980, Japanese Laid-open Utility Model Publication No. 47-33019 which was laid open to public inspection in 1972 and U.S. Pat. No. 3,633,063 which was patented on Jan. 4, 1972.